Transport software-defined networking (TSDN) may be considered to apply to the application of software-defined networking (SDN) techniques to the transport layers of a service provider Wide Area Network (WAN). The transport layers include layer 0 (L0) and layer 1 (L1), and possibly layer 2 (L2) in some cases. In the seven-layer Open Systems Interconnection (OSI) model of computer networking, the physical layer is L1 . The network cabling is sometimes referred to as L0. L0 may use, for example, Dense Wavelength Division Multiplexing (DWDM) or photonic transport systems. L1 may, for example, employ protocols such as Synchronous Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and Optical Transport Network (OTN). Layer 2 may be Ethernet.
A TSDN controller may monitor and manage traffic flows in the network.